From the Guidelines
In an 8-month-old with positive leukocyte esterase but negative nitrites on urinalysis, I recommend obtaining a urine culture and initiating empiric antibiotic therapy while awaiting results. The preferred empiric treatment is oral cefixime at 8 mg/kg/day divided twice daily, or amoxicillin-clavulanate at 40 mg/kg/day divided twice daily for 7-10 days, as suggested by 1. For febrile infants or those appearing ill, consider hospitalization for parenteral antibiotics (ceftriaxone 50-75 mg/kg/day). Positive leukocyte esterase indicates white blood cells in the urine, suggesting inflammation, while negative nitrites mean certain bacteria (particularly gram-negative organisms that convert nitrates to nitrites) may not be present. However, this pattern can still represent a urinary tract infection, as some pathogens don't produce nitrites or the urine may not have remained in the bladder long enough for nitrite production. Some key points to consider in the diagnosis and management of urinary tract infections in infants include:
- The sensitivity and specificity of leukocyte esterase and nitrite tests, as reported in 1
- The importance of urine culture in confirming the diagnosis, as emphasized in 1
- The need for careful assessment of the likelihood of UTI, as discussed in 1 After treatment, follow-up urinalysis is recommended to ensure resolution, and infants with confirmed UTI should undergo renal ultrasound to evaluate for anatomical abnormalities that might predispose to recurrent infections. It is also important to note that a negative urinalysis result does not rule out a UTI with certainty, as noted in 1. Therefore, clinical judgment and careful monitoring are essential in the management of febrile infants with suspected UTI.
From the Research
Urine Test Results
- The presence of leukocyte esterase in urine without nitrite can indicate a urinary tract infection (UTI) 2, 3, 4, 5.
- The sensitivity and specificity of leukocyte esterase test vary across different studies, with sensitivity ranging from 63.6% to 96.4% and specificity ranging from 44.2% to 95.8% 2, 4.
- In infants under 6 months, the leukocyte esterase dipstick has a sensitivity of 92% and specificity of 89.7% 4.
- The combination of leukocyte esterase and nitrite tests can improve the diagnostic accuracy of UTI, with a sensitivity of 75-84% and specificity of 82-98% 3.
Diagnostic Considerations
- Urine culture is considered the gold standard for diagnosing UTI, but it may take time to obtain results 2, 3.
- The presence of pyuria (white blood cells in urine) can also indicate UTI, with a sensitivity of 95.6% and specificity of 60.9% 2.
- In critically ill patients, leukocyte esterase and pyuria are the most sensitive indicators of a positive urine culture, with sensitivity of 87.5% and 73.3%, respectively 5.